The positioning of a heart cam type return-to-zero member, particularly for returning a chronograph counter to the zero position, generally requires the use of a jumper, which occupies considerable space and uses energy, or a flexible hammer or a hammer articulated in several parts.
The document CH 702 718 in the name of MONTRES BREGUET SA describes a time zone mechanism, arranged for displaying, on demand, the time in a particular time zone, on the main hands of a timepiece including:                two programmable memory wheels, each comprising a wheel including drive means for rotation about an axis of rotation, and a reversibly movable heart cam pivoting between indexing positions of said wheel,        means of support arranged for disengageable cooperation with a bearing surface comprised in each said memory wheel, and, between two actions by the user, engageably cooperating with said bearing surface of one of said memory wheels, and then being disengaged from said bearing surface of the other said memory wheel,        a differential gear with two inputs and one output, a first input being formed by a motion work wheel arranged to be driven by the movement, a second input being formed by a crown of the differential gear, and the output consisting of a cannon-pinion or an arbor carrying an hour hand, each of the memory wheels directly or indirectly meshing via the drive means with the differential crown.        